Newly-promoted Norwich stunned Manchester City 3-2 at Carrow Road on Saturday to inflict a first Premier League defeat on the English champions since January.
Kenny McLean, Todd Cantwell and the prolific Teemu Pukki took advantage of a ragged City defence without the injured Aymeric Laporte for a remarkable upset.
Defeat for City sees Pep Guardiola's men already fall five points behind European champions Liverpool -- who have a perfect record from their first five games -- in the title race.
City's decision not to strengthen at centre-back over the summer despite former captain Vincent Kompany's departure to become player-manager at Anderlecht could cost Guardiola's side the title with Laporte sidelined by a serious knee injury until at least January.
The City manager fielded his only two fit centre-backs John Stones and Nicolas Otamendi, but they struggled to cope and gifted Norwich back their two-goal lead at the start of the second-half after Sergio Aguero had reduced the arrears.
Guardiola's decision to rest Kevin de Bruyne will also be questioned as the visitors started slowly and were punished by a Norwich side that themselves had been ravaged by injuries.
Daniel Farke had to name two goalkeepers on his substitute bench just to make up the numbers, but the hosts were spurred as City's weakness at defending set-pieces was exposed when McLean rose highest to head home the opening goal.
It was 2-0 just before the half hour mark as Kyle Walker played Pukki onside and the Finn unselfishly squared for Cantwell to tap into an empty net.
City looked to have a route back into the game just before half-time when Bernardo Silva's cross picked out Aguero to continue his record of scoring in every game so far this season in the Premier League.
But the visitors' momentum was halted just five minutes after the restart.
Stones needlessly played Otamendi into trouble and the Argentine was robbed by Emiliano Buendia, who fed Pukki to prod home his sixth goal of the season.
Guardiola responded by throwing on De Bruyne and Gabriel Jesus, but it was not until Rodri drilled into the bottom corner two minutes from time that City looked like mounting a late comeback.
Aguero, Jesus and Raheem Sterling all fired too close to Tim Krul in the dying seconds as Norwich held out for a famous victory.